Evaluation of the Xpert Flu A Panel nucleic acid amplification-based point-of-care test for influenza A virus detection and pandemic H1 subtyping.

BACKGROUND: Influenza antigenic point-of-care (POC) tests are too insensitive for individual reliable diagnosis of influenza virus infections without additional laboratory confirmation. Molecular POC tests could be a valuable alternative.

OBJECTIVES: To evaluate the first influenza molecular POC test commercially available, the Cepheid Xpert Flu A Panel designed to simultaneously detect influenza A virus and subtype A(H1N1) 2009 pandemic virus, and compare it with in-house real-time RT-PCR (qRT-PCR).

STUDY DESIGN: Clinical specimens positive for influenza virus and influenza virus isolates with different viral loads and of different type and subtype were used to determine the analytical reactivity and sensitivity. A panel of pathogen negative specimens and isolates of 19 different respiratory pathogens were used to determine the analytical specificity.

RESULTS: Except A(H9N2) virus the Xpert Flu A Panel detected A(H1N1) seasonal and 2009 pandemic, A(H3N2), A(H5N2), A(H5N1) and A(H7N7) viruses and correctly subtyped A(H1N1) 2009 virus. Analytical sensitivity was similar to qRT-PCR in the range of 400-5000 viral particles per ml. However, of most subtypes some specimens with cycle threshold values greater than 30 in qRT-PCR and A(H1N1) 2009 specimens with inconsistent results in the qRT-PCR due to primer or probe mismatches were not detected in the Xpert Flu A Panel. Analytical specificity was 100%.

CONCLUSIONS: The Xpert Flu A Panel is the first commercially available POC molecular test for detection of influenza A virus and determination of the H1 2009 subtype and is analytically reasonable sensitive compared with qRT-PCR and highly specific and therefore a welcome alternative to antigenic POC tests.